The Isotopic Tracer and Resource Value of Microbial Gas Production in Coalbeds—A Case Study of Coalbed Gas in Enhong, China

From the new perspective of the dynamic isotopic fractionation of microbes and the mixture of secondary biogenic gas and thermogenic gas in coalbeds, this study evaluates the geochemical characteristics of mixed coalbed gas in Enhong. Additionally, by using isotopes, the study traces the microbial activities and the results of those activities, such as the methane production of bacteria, and reveals the formation mechanism and genetic types of coalbed gas. The measured δ13C1 values of the coalbed gas samples are from −54.5‰ to −32.0‰. Based on the values of Ro and δ13C2, by calculation, the δ13C1 values of thermogenic methane range from −30.6‰ to −28.1‰ and from −30.7‰ to −28.3‰, respectively. The results of the two calculations are highly consistent, and both are approximately 20‰ higher than the measured values. The measured δDCH4 values are from −217‰ to −196‰, being between thermogenic methane and microbiogenic methane; the δ13CCO2 values are from −30.5‰ to −23.9‰, growing heavier with respect to the ...